<template>
	  <div id="goTop">
        <div class="goTop" v-show="goTopShow" @click="goTop">
            <i class="iconfont icon-fanhuidingbu"></i>
        </div>
     </div>
</template>


<script>
	export default {
		name:'goTop',
	    data() {
        		return {
           		 scrollTop: "",
            		goTopShow: false
       		 }
   		 },
	    watch: {
	        scrollTop(val) {
	            if (this.scrollTop > 300) {
	                this.goTopShow = true;
	            } else {
	                this.goTopShow = false;
	            }
	        }
	    },
    methods: {
        handleScroll() {
            this.scrollTop =
                window.pageYOffset ||
                document.documentElement.scrollTop ||
                document.body.scrollTop;
            if (this.scrollTop > 500) {
                this.goTopShow = true;
            }
        },
        goTop() {
            let timer = null,
                _that = this;
            cancelAnimationFrame(timer);
            timer = requestAnimationFrame(function fn() {
                if (_that.scrollTop > 0) {
                    _that.scrollTop -= 50;
                    document.body.scrollTop = document.documentElement.scrollTop =
                        _that.scrollTop;
                    timer = requestAnimationFrame(fn);
                } else {
                    cancelAnimationFrame(timer);
                    _that.goTopShow = false;
                }
            });
        }
    },
    mounted() {
        window.addEventListener("scroll", this.handleScroll);
    },
    destroyed() {
        window.removeEventListener("scroll", this.handleScroll);
    }
}
	
</script>

<style scoped>
.goTop {
	    position: fixed;
	    width: 3.5rem;
	    height: 3.5rem;
	    line-height: 3.5rem;
	    right: 5%;
	    top: 70%;	    
	    border-radius: 50%;
	    background:rgba(200,200,200,0.6);
	    text-align: center;
	    cursor: pointer;
	    z-index: 10000;
	   
}

.icon-fanhuidingbu {
    color: deeppink;
     font-size: 2rem;
     
}
</style>